With the recent development of digital devices such as computers, it has become common to handle an enormous amount of computing data and two- and three-dimensional image data. There is a need to provide large-capacity high-speed memories and high-performance microprocessors for quick processing of such enormous information. Further, the processing power required of the digital devices is estimated to increase more and more as broadband spreads with the development of network systems such as the Internet.
In order to attain this need, various devices and equipment e.g. semiconductor devices are required to achieve higher density and higher integration. In particular, the requirements for photolithography techniques for fine patterning of the semiconductor devices are becoming more stringent year by year. For example, a photolithography process using ArF excimer laser radiation (wavelength: 193 nm) has been put into use in response to the requirement for patterning with a minimum line width of 0.13 μm or less for production of 1-Gbit or higher-capacity DRAMs. Further, the development of a photolithography process using 13.5-nm wavelength extreme ultraviolet (EUV) radiation has been pursued for finer patterning.
Although novolac resins and polyvinylphenol resins are conventionally used in resist compositions, these resins cannot be used in the above wavelength ranges because of too high light absorption. There have thus been examined, as alternative resist resins, acrylic resins (see e.g. Patent Document 1) and cycloolefin resin resins (see e.g. Patent Document 2).
In the case of forming a pattern by the use of a photoresist composition, it is preferable to utilize an aqueous tetramethylammonium hydroxide (TMAH) solution, rather than an organic solvent, as a developer in consideration of environmental issues. Herein, a phenolic hydroxyl group, a carboxyl group and a hexafluoroisopropanol group are each known as a functional group soluble in the aqueous TMAH solution, i.e., developable with the aqueous TMAH solution. For use of a photoresist composition by exposure at an ArF laser wavelength (193 nm) or a F2 laser wavelength (157 nm), the introduction of a carboxyl group or a hexafluoroisopropanol group to a resist resin has mainly been examined in view of the fact that an aromatic ring has a strong wide absorption band in these wavelength ranges. When the resist resin has a hexafluoroisopropanol functional group, the resulting resist composition shows good developability and substrate adhesion properties and attains a relatively favorable pattern profile in fine patterning process. However, special specific synthesis techniques are required for the synthesis of such a hexafluoroisopropanol-containing resin. On the other hand, when the resist resin has a carboxyl functional group, it is difficult to form a desired pattern by the use of such a carboxyl-containing resist resin as the carboxyl-containing resin is swelled in the TMAH solution (see Patent Document 3).
There have further been known, as carboxylic acid compounds with α-position fluorine, 2-fluoro-phenylacetic acid and ester thereof (see Patent Document 4) and ethyl-2,2-difluoro-3-hydroxy-3-phenylpropionic acid (see Non-Patent Document 1).